JPH0337218A - Production of blocked polyisocyanate and polyurethane composition - Google Patents

Abstract

PURPOSE:To obtain a one-pack polyurethane coating material which can give a coating film excellent in weather resistance, impact resistance and flex resistance by blocking an NCO-terminated prepolymer obtained from a specified polyester polyol and a diisocyanate compound. CONSTITUTION:An NCO-terminated prepolymer is obtained by reacting a polyester polyol (A) (of a number-average mol.wt. of 500-2000 and an average OH functionality of 2-3) with an excess of aliphatic and/or alicyclic diisocyanate (B) (desirably 1,6-hexamethylene diisocyanate) at 80-140 deg.C in an NCO to OH equivalent ratio of desirably 5-40. A blocked polyisocyanate is produced by blocking the terminals of this prepolymer with a blocking agent (e.g. methyl ethyl ketoxime). This blocked isocyanate is mixed with a polyhydroxy compound (e.g. Acrydic A801, a product of DaiNippon Ink) in an equivalent ratio of the latent NCO to the hydroxyl of 0.5-2 to obtain a one-pack thermosetting polyurethane composition.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a block polyester, which is obtained by blocking the terminal isocyanate groups of a prepolymer consisting of a polyester polyol and an aliphatic and/or alicyclic diisocyanate with a blocking agent. The present invention relates to a method for producing isocyanate, and a single-wave type polyurethane thermosetting composition comprising the blocked polyisocyanate and a polyhydric hydroxyl compound and having excellent flexibility and weather resistance.

[Conventional technology]

Polyurethane paints have very good abrasion resistance, chemical resistance, and stain resistance, and polyurethane paints using polyisocyanates derived from aliphatic and cycloaliphatic diisocyanates have even more It has excellent weather resistance, and its demand is on the rise.

However, since the polyurethane paint -i is a two-component paint, it is extremely inconvenient to use.

That is, a typical polyurethane paint consists of two components, a polyol component and a polyisocyanate component, and it is necessary to store them separately and mix the two components at the time of painting. Furthermore, the current situation is that paints once mixed become gelled within several hours to several days and become unusable. This makes it extremely difficult to perform automatic painting in fields where line painting is performed, such as automobile or home appliance painting.

In order to improve the drawbacks of the two-component polyurethane paints, it has been proposed to use pro-nocturnal isocyanate whose active isocyanate groups are blocked with an active hydrogen-containing compound (blocking agent). This blocked polyisocyanate does not react with polyols at room temperature, but
At a relatively high temperature, the blocking agent is dissociated and the active isocyanate groups are regenerated and react with the polyol to cause a crosslinking reaction, so that the above-mentioned drawbacks can be improved to some extent.

Therefore, a large number of block polyisocyanates have been investigated. Many block bodies are known, such as Japanese Patent Publication No. 38380). In addition, active hydrogen-containing compounds such as phenol-based, lactam-based, and oxime-based compounds are known as blocking agents.

[Problem to be solved by the invention]

The conventionally known block bodies of billet type polyisocyanate and block bodies of isocyanurate type polyisocyanate have a glass transition temperature of 2.
When combined with a polyol of 0 to 100"C, weather resistance is good, but there are problems with flexibility, impact resistance, bending resistance, etc. For this reason, one-component type with no limit on pot life. There has long been a need for a single-wave polyurethane thermosetting composition that not only has good weather resistance but also provides a coating film with excellent resilience, impact resistance, and bending resistance.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present inventor has completed the present invention as a result of extensive research into block polyisocyanates that provide polyurethane coatings with excellent weather resistance and flexibility.

That is, the present invention has a number average molecular weight of 1500 to 2.000.
A polyester polyol having an average number of hydroxyl groups in one molecule of 2 to 3 is reacted with an excess amount of aliphatic and/or alicyclic diisocyanate to form an isocyanate group (NCOl) at the end.
The present invention relates to a method for producing a blocked polyisocyanate, in which a prepolymer having the following properties is produced, and then the ends of the prepolymer are blocked with a blocking agent, and a composition comprising the blocked polyisocyanate and a polyhydric hydroxyl compound.

This composition provides a polyurethane coating with excellent weather resistance, flexibility, impact resistance, and flex resistance.

The diol or triol constituting the polyester polyol having an average number of 2 to 3 hydroxyl groups in a number average molecule of 1500 to 2,000.1 molecules used in the present invention has 2 to 3 carbon atoms.
Those having up to 20 linear or branched alkyl groups can be used. Typical examples include ethylene glycol, propylene glycol, 1,4-butanediol, 1,3-butanediol, 1,5-bentanediol, neopentyl glycol, 1.6-hexanediol, 1.8- Octanediol, 2,2,4-trimethyl-1,3bentanediol, glycerin, trimethylolpropane, etc. can be used. The amounts of diols and triols used are adjusted depending on the desired average number of hydroxyl groups.

Further, when a diol or triol having a branched alkyl group is used, the solvent solubility of the resulting polyester polyol and the compatibility with the polyhydric hydroxyl compound used as the main ingredient are favorably influenced.

In addition, the number average molecule used in the present invention is 1,500 to 2,000.
．． As the carboxylic acid constituting the polyester polyol having an average number of hydroxyl groups in one molecule of 2 to 3, a dicarboxylic acid having 2 to 20 carbon atoms is used. Examples include adipic acid, azelaic acid, and sebacic acid. Aromatic dibasic acids such as isophthalic acid and terephthalic acid may also be used, but they must be used within a range that does not impair the flexibility of the blocked polyisocyanate of the present invention.

The polyester polyol of the present invention comprises the above diol/
It is produced by an esterification reaction using raw materials such as triol and dicarboxylic acid using a conventional method, usually at a temperature range of 100 to 250°C, and its number average molecular weight must be in the range of 500 to 2,000. . A coating film using a prepolymer block consisting of a polyester polyol and diisocyanate having a number average molecular weight of less than 500 has poor flexibility. Furthermore, when a polyester polyol with a number average molecular weight exceeding 2.000 and a diisocyanate are used, the content of latent NGO groups after forming into a block is too low to be practical, and furthermore, it is difficult to compatibility with polyvalent hydroxyl compounds. It tends to decrease solubility.

In the present invention, the number average molecular weight of the polyester polyol is determined by measuring the hydroxyl value and using the following formula.

Hydroxyl value: Value N measured according to 6.4 of JIS 4-1577: Average number of hydroxyl groups in one molecule of polyester polyol As the diisocyanate in the present invention, aliphatic and/or alicyclic diisocyanate is used. It will be done.

In addition, as the aliphatic diisocyanate, carbon number 4 to 3
As the alicyclic diisocyanate, those having 8 to 30 carbon atoms are preferably used.

Examples of aliphatic or cycloaliphatic diisocyanates include 1
．． 4-tetramethylene diisocyanate, 1.5-pentamethylene diisocyanate, 1,6 hexamethylene diisocyanate, 2.2.4-trimethyl-1,6-hexamethylene diisocyanate, lysine diisocyanate , 3-isocyanatomethyl-3,5,5-trimethylcyclohexyl isocyanate (isophorone diisocyanate), 1,3-bis(isocyanatomethyl)-
Examples include cyclohexane and 4,4'-dicyclohexylmethane diisocyanate. Among these, 1,6-hexamethylene diisocyanate is preferred in terms of weather resistance and industrial availability.

The reaction between the polyester polyol and the aliphatic and/or alicyclic diisocyanate is carried out as follows.

The reaction temperature ranges from normal temperature to 200°C, preferably from 80°C to
It is carried out in the range of 140"C. If the reaction temperature is low, it will take too long for the reaction to complete; on the other hand, if the reaction temperature exceeds 200"C, undesirable side reactions will occur and the viscosity of the prepolymer will increase. This is not practical because the prepolymer produced is markedly colored.

During the reaction, no solvent may be used, or any solvent inert to the isocyanate group may be used. Further, if necessary, a catalyst may be used to promote the reaction between the isocyanate group and the hydroxyl group.

During the reaction, the equivalent ratio of the diisocyanate and polyester polyol to be charged is preferably NGO1011 ratio 5 to 40. If this equivalent ratio is less than 5, a sequential addition reaction will occur between the diisocyanate and the polyester polyol, resulting in the formation of a polymer. is formed, which increases the viscosity of the prepolymer. This increase in viscosity makes removal of unreacted diisocyanate difficult. In addition, a highly viscous prepolymer block has poor compatibility with a polyhydric hydroxyl compound and poor flexibility. Moreover, if the NGO10H equivalent ratio exceeds 40, it is not preferable because productivity will deteriorate.

When the reaction is completed, unreacted diisocyanate in the reaction mixture is recovered by a known method such as a thin film evaporator or solvent extraction. If the residual amount of unreacted diisocyanate is large, problems such as odor, toxicity, irritation, etc. due to the diisocyanate monomer will arise during heat curing.

Next, the blocked polyisocyanate of the present invention can be obtained by reacting the aforementioned NGO group-terminated prepolymer with various blocking agents by a known method.

Blocking agents used in this reaction include, for example, phenol-based, lactam-based, oxime-based, active methylene-based, alcohol-based, mercaptan-based, acid amide-based, imide-based, amine-based, imidazole-based, and urea-based blocking agents. Blocking agents such as phenolics, lactams, oximes and the like are advantageously used. Specific examples of blocking agents include the following.

Phenol blocking agents: Phenol 1, cresol, xylenol, ethylphenol, etc. Lactam blocking agents: ε-caprolactam, δ-valerolactam, β-butyrolactam, β-propiolactam, etc. Oxime blocking agents: Formamide Oxime, acetamidoxime, acetoxime, methyl ethyl ketoxime, diacetylmonoxime, benzophenone oxime, cyclohexanone oxime, etc. Active methylene blocking agents: diethyl malonate, dimethyl malonate, ethyl acetoacetate, methyl acetoacetate, acetylacetone, etc. , Alcohol blocking agent: methanol, ethanol, propanol, isopropanol, butanol, 2-ethylhexanol, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, etc.

As a specific method for producing the blocked polyisocyanate of the present invention, the NCOi-terminated prepolymer and the blocking agent are mixed in an equivalent ratio of NCO group/active hydrogen in the blocking agent of 0.9 to 1. O1 preferably 0.95 to 1.05
The reaction is carried out by a method known in the art.

Although this blocking reaction can be carried out without a solvent, it is preferably carried out in a suitable solvent, such as an ester, ether, ketone, or aromatic solvent, which does not contain active hydrogen. Furthermore, in the reaction, organic metals such as tin, zinc, and lead, tertiary amines, and the like may be used as catalysts.

In the present invention, examples of the polyhydric hydroxyl compound used include acrylic polyols, fluorine-containing polyols, polyester polyols, and the like.

These polyols can also be used as a mixture as appropriate.

(2) The acrylic polyol used as the polyhydric hydroxyl compound in the present invention is obtained by copolymerizing a polymerizable monomer having one or more hydroxyl groups in one molecule and another monomer copolymerizable with the monomer. Examples of these include acrylic acid esters with active hydrogen such as 2-hydroxyethyl acrylate, 2-hydroxypropyl acrylate, and 2-hydroxybutyl acrylate; 2-hydroxyethyl methacrylate, methacrylate Methacrylic acid esters with active hydrogen such as 2-hydroxypropyl acid and 2-hydroxybutyl methacrylate; or acrylic acid monoester or methacrylic acid monoester of glycerin, acrylic acid monoester or methacrylic acid monoester of trimethylolpropane Single or mixtures selected from the group of esters; methyl acrylate, ethyl acrylate, isopropyl acrylate,
Acrylic acid esters such as n-butyl acrylate and 2-ethylhexyl acrylate; methyl methacrylate, ethyl methacrylate, isopropyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-hexyl methacrylate, methacrylate Examples include singly or a mixture selected from the group of methacrylic acid esters such as lauryl acid.

In addition, as necessary, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, maleic acid, and itaconic acid; unsaturated amides such as acrylamide, N-methylolacrylamide, and diacetone acrylamide; and glycidyl methacrylate, styrene, Three polymerizable monomers selected from the group of polymerizable monomers such as vinyltoluene, vinyl acetate, and acrylonitrile may be added alone or in combination.

The copolymerization of the hydroxyl group-containing acrylic monomer and the radically polymerizable unsaturated monomer can be carried out according to a method known per se, for example, by a solution polymerization method. Polymerization is generally carried out by combining the above two or more monomer components in a suitable solvent, such as toluene, xylene, ethyl acetate, butyl acetate, etc., in the presence of a polymerization catalyst, usually for 40 to
This can be carried out by reacting at a reaction temperature of 170°C for 4 to 10 hours.

Further, as the polymerization catalyst, for example, common initiators for radical polymerization such as azo compounds, peroxide compounds, diazo compounds, redox compounds, etc. can be used.

The acrylic polyol used in the present invention can be made to have a desired glass transition temperature and hydroxyl value by appropriately selecting the type and amount of the polymerizable monomer and the type and amount of the hydroxyl group-containing monomer.

In addition, commercially available acrylic polyols include Acrydike A301, Acrydike A30F (manufactured by Daienhon Ink Chemical Industry ■, trade name), Hydaloid 3008, Hydaloid 3083 (manufactured by Hitachi Chemical ■, trade name), Cortax LH-601, L) l-657 (manufactured by Toshi ■, product name)
etc.

■ The fluorine-containing polyol used as the polyhydric hydroxyl compound in the present invention is, for example, JP-A-57-3410
Publication No. 7, JP-A-57-34108, JP-A-61
JP-A-59-41, which contains fluoroolefins as a tctc component, as seen in Japanese Patent Publication No. 176620, etc.
321, JP-A No. 59-96177, and JP-A-61-118466, further modified fluorine-containing polyols having the above-mentioned fluoroolefins as constituent components, Examples include those in which an unsaturated monomer having a fluorine-containing group in the side chain is used as a constituent component, as seen in Japanese Patent No. 5834866.

The fluorine-containing polyol used in the present invention can be made to have a desired glass transition temperature and hydroxyl value by appropriately selecting the type and amount of the polymerizable monomer and the type and amount of the hydroxyl group-containing monomer.

Commercially available fluorine-containing polyols include Le ξ Flon LP-100, Lumiflon LP-200 (manufactured by Asahi Glass ■, trade name), K-700, K-701 (manufactured by Ohme Mizu Ink Chemical Industry ■, trade name). etc. can be mentioned.

■ Examples of polyester polyols that can be used as the polyhydric hydroxyl compound of the present invention include carboxylic acids such as succinic acid, adipic acid, sebacic acid, dimer acid, maleic anhydride, phthalic anhydride, isophthalic acid, and terephthalic acid. A single or a mixture of dibasic acids selected from the group, and a single or a mixture of polyhydric alcohols selected from the group of ethylene glycol, propylene glycol, diethylene glycol, butylene gellicol, neopentyl glycol, trimethylolpropane, glycerin, etc. Examples include polyester polyols obtained by a condensation reaction.

The polyester polyol of the present invention can be produced by appropriately changing the type and charging ratio of dibasic acid and polyhydric alcohol.
It can be made to have a desired glass transition temperature and hydroxyl value.

As a commercially available polyester polyol, Parnock D
6-439, Parnock D-220 (manufactured by Dainippon Ink & Chemicals, trade name), and the like.

The polyvalent hydroxyl compound used in the present invention preferably has a glass transition temperature (Tg) of 20°C to 100°C. If a compound with a Tg of more than 100°C is used, the flexibility will not be good.On the other hand, if a Tg is less than 20''C, there will be a problem in weather resistance.In addition, the hydroxyl value of the polyhydric hydroxyl compound used in the present invention is 10 to 1 based on resin.
The range of 50 mgKOR/g is preferable, and the hydroxyl value is 1
If it is smaller than 0, the crosslinking density in the coating film becomes small,
Those with poor solvent resistance and hydroxyl value exceeding 150 have problems with flexibility. Furthermore, the polyhydric hydroxyl compound used in the present invention has a number average molecular weight of 11,300 to 30
．． 000 is preferably used.

The composition of the present invention is blended so that the equivalent ratio of latent NCQ groups in the block polyisocyanate to hydroxyl groups in the polyhydric hydroxyl compound is 0.5 to 2. If this equivalent ratio is less than 0.5, solvent resistance and weather resistance will be poor, and if it exceeds 2, flexibility will be poor.

The compositions of the present invention typically contain organic compounds such as ethyl acetate, butyl acetate, toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, ethylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, etc. It is used diluted with MM.

In addition, as necessary, various stabilizers such as colored pigments, extender pigments, dispersants, antifoaming agents, leveling agents, transverse agents, catalysts for accelerating curing, hindered amines, hindered phenols, benzotriazoles, etc. Agents may also be added.

The composition of the present invention is cured by heating at a temperature of usually 50 to 250'C, preferably 100 to 200'C, for 1 to 120 minutes.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to synthesis agents and examples, but the present invention is not limited by these.

Incidentally, the analysis and evaluation of the coating film were performed by the following method.

■Prepolymer NCO content based on JIS-1556 ■Elongation at break based on JIS-6301 ■Bending resistance test based on JIS-5400 il (using 1/2 inch mandrel) ■11J impact test JIS- ni-5400 semi-1 (1 part 2 inches x 500g x 500mm) ■QU
V accelerated weathering test ASTM-G-53-77 compliant. In addition, gloss measurement is performed by JI
According to S-Z8741.

■Unreacted 11MDI Gas Chromatography Method ■Infrared Absorption Spectrum Measurement was performed using a sample coated on a rock salt plate according to a conventional method.

(Apparatus: FT/TR-5M, manufactured by Kuchimoto Bunko Co., Ltd.) ① Thermobalance measurement Measurement was carried out at a heating rate of 10"C/min using air (250 ml/min) as the atmospheric gas.

(Apparatus 5SC-5000TG/DTA200 manufactured by Seiko Electronics Co., Ltd.) Example 1 of artificial synthesis of polyester polyol In a flask equipped with a thermometer, cooler, stirrer, and nitrogen introduction front,
450 parts of 1,4-butanediol and 584 parts of adipic acid were charged and reacted at 220°C for 10 hours using a conventional method.
Acid value 4.5■KOI(/g, hydroxyl value 110mgKOI)
820 parts of a polyester polyol having an average number of hydroxyl groups of 2 per molecular weight (H/g) was obtained. The number average molecular weight of polyester polyol calculated from the hydroxyl value is 1.0
It was 20.

Synthesis Example 2 The same procedure as Synthesis Example 1 was performed except that 135 parts of 1,4-butanediol, 177 parts of 1,6-hexanediol, 156 parts of neopentyl glycol, and 526 parts of adipic acid were used. As a result, acid value 5.0 KOH/g, hydroxyl value 1
11■KO) l/g, the average number of hydroxyl groups in one molecular weight is 2
804 parts of polyester polyol were obtained. The number average molecular weight of the polyester polyol calculated from the hydroxyl value was 1.010.

Example 1 of Pro-Kuboi Isocia - A thermometer, condenser, stirrer, and a flask equipped with a nitrogen introduction front.
300 parts of the polyester polyol obtained in Synthesis Example 1,
1.6-hexamethylene diisocyanate (HMDI)
741 parts were charged and reacted at 100°C for 10 hours with stirring.

The reaction solution thus obtained was heated to 0.8 mmHg/160°C for the first time and 0.2 m for the second time using a thin film evaporator.
Unreacted HMDI was removed under mHg/160°C conditions.

374 parts of prepolymer were obtained with an NGO content of 6.2% and unreacted HMDI of 0.2%.

Next, prepolymer 30 from which unreacted HMD I had been removed was placed in a flask equipped with a thermometer, condenser, stirrer, and nitrogen introduction.
0 parts, 113 parts of ethyl acetate, and 39.3 parts of methyl ethyl ketoxime as a blocking agent, and heated at 50"C for 2 hours.
A blocked polyisocyanate solution was obtained by reacting for a period of time.

Latent NGO of the obtained blocked polyisocyanate solution
The content was 4.1% and the solid content was 75%.

After removing the solvent from the obtained blocked polyisocyanate, an infrared absorption spectrum was measured.

The results are shown in FIG. As shown in Figure 1, the NGO group reacts with the blocking agent, and the N
No absorption of GO groups was observed. Furthermore, the results of thermobalance measurements are shown in FIG. It can be seen that the blocking agent dissociates from around 180°C.

Example 2 300 parts of the polyester polyol obtained in Synthesis Example 2,
The reaction was carried out in the same manner as in Example 1, except that 747 parts of HMD I was used. The obtained reaction solution was applied to a thin film evaporator in the same manner as in Example 1, and the NGO content was 6.2% and the unreacted HMD
377 parts of a prepolymer containing 0.1% I was obtained. 300 parts of prepolymer, 113 parts of ethyl acetate, and 39.5 parts of methyl ethyl ketoxime were charged and reacted at 50''C for 2 hours to obtain a block polyisocyanate solution with a latent NGO content of 4.1% and a solid content of 75%. Ta.

Comparative Example 1) Isocyanurate type polyisocyanate derived from IMDI (manufactured by Asahi Kakai Kogyo Co., Ltd., Duraney) T
PA-100, NGO content 23.1%) 3oO parts, ethyl acetate 149 parts, and methyl ethyl ketoxime 147 parts were reacted in the same manner as in Example 1 to obtain a latent NGO content of 11.6% and solid content of 75%. A blocked polyisocyanate solution was obtained.

) Example 3 Acrytik A301 (
Manufactured by Dainippon Ink & Chemicals Co., Ltd., acrylic polyol, solid content = 50%, hydroxyl value = 50 KOH/g,
Tg = 70°c) 50 parts, 45.7 parts of the blocked polyisocyanate solution prepared in Example 1 as a blocked polyisocyanate solution, 10% by weight as a curing accelerating catalyst
After blending 2.8 parts of a xylene solution of dibutyltin dilaurate, methyl isobutyl ketone/
Xylene (weight ratio 50150) was added and prepared in a #4 Ford cup for 15 seconds to obtain a single wave thermosetting composition. This was cured with an air spray gun to a dry film thickness of 50 tons.
It was coated so that it became t, and was cured at 140°C for 40 minutes.

The elongation at break of the resulting coating film at 20°C was 94%, and -2
No cracks were observed in the bending resistance test and impact resistance test at 0°C. 1000 in mouth UV accelerated weather resistance test
The gloss retention rate after hours was 95%.

Example 4 The same procedure as in Example 3 was conducted except that 50 parts of Acrytik A301 and 45.7 parts of the blocked polyisocyanate solution prepared in Example 2 were used.

The elongation at break of the resulting coating film at 20°C was 125%, and -
No cranking was observed in the bending resistance test and impact resistance test at 20°C. 10 in QUV accelerated weathering test
The gloss retention rate after 00 hours was 96%.

Comparative Example 2 The same procedure as in Example 3 was carried out except that 100 parts of Acrytik A301 and 32.2 parts of the blocked polyisocyanate solution of Comparative Example 1 were used.

The elongation at break of the resulting coating film at 20°C was 3%, and -
Crank occurrence was observed in the impact resistance test and bending resistance test at 20°C.

〔Effect of the invention〕

The block polyisocyanate obtained by the method of the present invention is a novel block polyisocyanate that not only has good weather resistance but also provides a polyurethane coating film with excellent impact resistance and bending resistance. Furthermore, the single-wave polyurethane thermosetting composite sole of the present invention using this block polyisocyanate can be applied to coated objects such as metals and resin products. In particular, it is advantageously used for coating precoated metals and various plastics that require impact resistance and bending resistance.

[Brief explanation of drawings]

FIG. 1 shows the results of an infrared absorption spectrum after removing the solvent from the blocked polyisocyanate obtained in Example 1. FIG. 2 is a graph of the results of thermobalance measurement after removing the solvent from the blocked polyisocyanate obtained in Example 1. Figure 1 Figure 2

Claims (1)

[Scope of Claims] 1. A polyester polyol having a number average molecular weight of 500 to 2,000 and an average number of hydroxyl groups in one molecule of 2 to 3 is reacted with an excess amount of aliphatic and/or alicyclic diisocyanate, and the terminal A method for producing blocked polyisocyanate, in which a prepolymer having isocyanate groups is produced, and then the ends of the prepolymer are blocked with a blocking agent. 2. A polyester polyol with a number average molecular weight of 500 to 2,000 and an average number of hydroxyl groups in one molecule of 2 to 3 is reacted with an excess amount of aliphatic and/or alicyclic diisocyanate to have an isocyanate group at the end. A one-component polyurethane thermosetting composition prepared by producing a prepolymer and then blending a blocked polyisocyanate obtained by blocking the ends of the prepolymer with a blocking agent and a polyhydric hydroxyl compound.